The invention described herein relates to timing devices for electrical power circuits like lighting and appliance circuits in residences. In recent years a large demand for automatic and/or remote control of residential lighting has developed as a result of the increased crime rate involving home invasions. Automatically timed controlled of lighting has become widely accepted as a significant deterrent for prevention of home invasion. Also, the remote operation of lights, either automatically, from an intrusion alarm system, or from a remote location such as a bedside unit, is a desirable feature of a home protection system.
Automatic light timers commonly available today are motor driven mechanically activated switches. The least expensive type provides a single "on" time selection and a single "off" time selection for each 24-hour period. Some mechanical timers provide for the selection of one hour "on" or "off" intervals that can be arranged in any pattern. The pattern is repeated every 24 hours. The most popular timer type is self contained, with a two-prong plug integral with a housing therefor for directly plugging into the usual household electrical outlet. The housing also has an integral socket for plugging in the lamp or appliance to be controlled. Another timer type has a power cord and is designed for setting on the floor or table top. Some manufacturers offer timers for permanent wall mounted installation to control lighting fixtures. To further enhance the usefulness of automatic light timers as a deterrant against home invasions, some timers have a feature that alters the actual "on" time from day to day so that a more probable "lived in" pattern results.
Mechanical motor driven timers have achieved great popularity because of their low cost. However, because of the limitations of mechanical systems, mechanical timers presently in use suffer from a number of disadvantages. Thus, mechanical timers tend to be unreliable and noisy (especially after some period of use), forcing many owners to abandon their use in quiet areas such as studies and bedrooms. Mechanical timers are also large and bulky and therefore have not lent themselves widely to convenient table-top use with "decorator" type styling. The size and bulk of mechanical timers precludes their installation into a flush device electrical box, such as commonly houses wall switches for the control of outdoor or ceiling lighting fixtures.
Inexpensive mechanical timers have "MANUAL/AUTOMATIC" settings on a switch selector. When the timer is in the "AUTOMATIC" mode usually the light cannot be turned on or off without taking the timer out of the "AUTOMATIC" mode. Thus if it is desired to change the light from its present automatically programmed state to the opposite state (ON to OFF or OFF to ON) the user must remember to return to "AUTOMATIC" before leaving the room if he wants programmed control to continue. However, some mechanical timers heretofore developed have an automatic override feature where the automatic control returns to operation automatically when the manual setting and automatic setting subsequently correspond.
It is, accordingly, one of the objects of the invention to provide a timer, which has its most important but not its only application to automatically energize and de-energize home lighting, entertainment equipment or appliance circuits, and wherein the timer is capable of providing a number of "on" and "off" intervals over a 24-hour period by electrical control circuitry which may be made in the form of integrated circuits, so that the resulting timer operates quietly and can be made in a very compact and attractive form, and wherein a measure of variability is automatically provided in the pattern of such "on" and "off" intervals from one day to the next. A timer which if unattended actuates a load device such as an externally visible interior electric light in, for example, a dwelling, according to an invarying on-off pattern (hereinafter referred to as the duty profile) from one day to the next is considered to present to an external observer an inadequate illusion of occupancy. A precise daily repetition of the stored program would, it is believed, be readily noted.
A mechanical timer which automatically varies the duty profile on successive days is the "Super-Cop" timer marketed currently by Sears-Roebuck, Inc. (Model No. 796.664000). This unit, however, produces only a single cycle, i.e. one off-on-off transition pattern at two mechanically presettable times, said times being preset by manually positioning two tabs on the face of a graduated 24-hour rotating dial. Dogs attached to the tabs engage canes on a camshaft to intermittently rotate the camshaft to actuate a simple microswitch. By appropriate cam shaping, the actuation cycle is displaced in time by a fixed number of minutes on alternate days, the duty profile cycle thereby repeating every 48 hours.
There has been described in a co-pending application by R. Goldstein and L. Schornack entitled "Timer and Power Control System," Ser. No. 22,453 filed Mar. 21, 1979, an invention relating to a programmable timer. The electric timer of that invention is a 24-hour repeat cycle timer which controls an external load device such as an electric light according to a bit pattern stored in a memory unit which may be a random access memory, but which is most advantageously a recirculating bit shift register having the same number of stages as the number of basic programmable time intervals, e.g. 15 or 30 minutes, over a 24-hour period. Output sensing from a selected register stage actuates a triac, which in turn actuates the load device. The bit pattern is advanced automatically at the regular basic timing intervals by internal timing means. A pushbutton override allows the user to turn the load device on or off while the timer is in operation without disturbing the stored pattern. In one mode of operation rapid programming in a manner of a minute or so may be achieved by rotating a dial knob. In another mode of operation, real time programming is achieved during the first 24 hours after the timer is activated by application of power in accordance with the load device on and off duty profile as obtained by the normal operation of the pushbutton used as a normal on and off control.
Another and more specific object of the invention is to vary the duty profile of such a timer in such a way that if the stored program is unchanged from one day to the next, the duty profile is different for any two consecutive days.